In recent years, the place of heavy cast iron, steel and concrete pipe has largely been taken over by pipe made by the extrusion of plastic materials which are not only lighter in weight but appear to have comparable resistance to deterioration in certain applications such as drainage and soil work.
Pipes of this type, having diameters in the range of two inches or more, usually are formed in sections of uniform length, one end of each section having a radial enlargement, or bell, sufficient to receive the unenlarged end of another similar pipe.
The inside diameter of the bell is sufficiently large to easily receive the end of the next section of pipe and may be large enough to allow a sealing material to be packed in around the joint. In other cases, the bell may be provided with an internal annular recess into which a sealing material, such as a ring of resilient material, is inserted, and the adjacent pipe end is forced in beyond the sealing ring. However, difficulty has been experienced in the formation of the annular recess in such bells because it requires the use of apparatus capable of deforming outwardly only a portion of the axial length of the bell while the material is in a plastic condition, and removing the apparatus after the plastic has solidified.
Multi-section expanding cores having two dissimilar groups of interfitting core sections are known but these devices usually require one of the groups of core sections, or an elongated wedge-like expander, to be moved in an axial direction during contraction and expansion. Other types of core means are known in which one, or both, of the core sections pivot about axes which are axially remote from the plane of their radial movement. In both cases, it is difficult to maintain either circumferential or radial alignment of the core sections in their expanded positions with the result that irregularities are produces in the internal annulus produced in the finished pipe bell, which irregularities have a deleterious effect on a sealing ring inserted therein as well as on the effectiveness of the seal itself when the adjacent pipe end is in place. Moreover, the equipment made in accordance to the prior art often is bulky and complex in construction, and the actuating mechanisms, in particular, are complex and lacking in ease and precision of control.
Therefore, an object of the present invention is to provide a mandrel of the type having two groups of expandable and contractible core sections for producing an outwardly deformed annulus on a plastic pipe bell, in which the core sections remain at all times in the same common radial plane and in which these sections do not tilt in any way during their movement in contraction and expansion, and in particular, to provide an improved and simplified actuating mechanism in such a mandrel that is positive and precise in its operation.